Heat treated ferromagnetic particles

ABSTRACT

FERROMAGNETIC ALLOY PARTICLES OF IRON, NICKEL OR COBALT, AND OPTIONALLY CHROMIUM SUPERSATURATED WITH BORON, NITROGEN OR PHOSPHORUS WHICH ARE PREPARED BY REDUCTION OF A SOLUTION CONTAINING SALTS OF THE APPROPRIATE METALS, ARE CONVERTED TO POLYPHASE PARTICLES OF SUBSTANTIALLY UNCHANGED SIZE HAVING IMPROVED MAGNETIC PROPERTIES BY HEATING BELOW THEIR SINTERING TEMPERATURES. THE FERROMAGNETIC PARTICLES ARE USEFUL FOR MAKING MAGNETS AND FOR MAKING MAGNETIC RECORDING MEMBERS.

March 2', 1971 a GRAHAM EI'AL 3,567,525

HEAT TREATED FERROMAGNETIC PARTICLES Filed June 25. 1968 3 Sheets-Sheet 1 March 2, 1971 A. H. GRAHAM ETAL 6 3,557,525

' HEAT TREATED FERROMAGNETIC PARTIEJLYES, Filed Jufles. 1968 SShee ts-Shee t-Z 0 a 4- '6 e 1a 2a l4 l6 77M6/HRJ March 2, 1 971 A. H. GRAHAM ETAL 3,567,525.

' HEAT TREATED FERROMAGNETIC PARTICLES v Filed June 25, 1968' 3 Sheets-Sheet 5 o e 4 6 9 1o x2 19 /6 TIME/FIR) Q c 300 c 80o 600 .H c X \c a. 200 c 0 a 4 6 8 la /8 W /5 United States Patent 3,567,525 HEAT TREATED FERROMAGNETIC PARTICLES Arthur Hughes Graham, Ernest Lewis Little, Jr., and Jack D. Wolf, Wilmington, Del., assignors to E. I. du Pont de Nemours and Company, Wilmington, Del.

Filed June 25, 1968, Ser. No. 739,732 Int. Cl. C21d 1/04; H01f 1/06, 7/02 U.S. Cl. 148-3157 10 Claims ABSTRACT OF THE DISCLOSURE Ferromagnetic alloy particles of iron, nickel or cobalt, and optionally chromium supersaturated with boron, nitrogen or phosphorus which are prepared by reduction of a solution containing salts of the appropriate metals, are converted to polyphase particles of substantially unchanged size having improved magnetic properties by heating below their sintering temperatures. The ferromagnetic particles are useful for making magnets and for making magnetic recording members.

FIELD OF THE INVENTION Miller and Oppegard, in US. Pat. 3,206,338 have described the preparation of boron-containing acicular particles of iron, or alloys of iron with cobalt and/or nickel by the reduction of solutions of the appropriate metal salts with an alkali or aikaline earth metal hydride. In copending application Ser. No. 739,860, now abandoned it has been disclosed that up to 20% by weight of metallic chromium can be incorporated into the ferromagnetic particles of Miller and Oppegard, by incorporating a suitable salt of chromium in the mixture of metallic salts that are reduced. Similar compositions containing nitrogen or phosphorus are disclosed hereinafter.

The above ferromagnetic particles consist of a supersaturated solid solution of the boron, nitrogen or phosphorus in an alloy of the metals, with a coating of metal oxide and/or adsorbed moisture on the surface of the particles. It has now been discovered that the chemical constitution of the particles can be modified and the magnetic properties improved by a heat treatment process, while maintaining the fine particle size.

SUMMARY OF THE INVENTION The novel products of the present invention are defined A ferromagnetic composition comprising polyphase, non-pyrophoric particles generally having single domain behavior and having a maximum dimension of about 4 microns, said particles consisting of at least one metal consisting of iron, cobalt and nickel, and from to 20% chromium and at least one of B,N or P, in an amount less than the minimum amount required to form a compound with all of said metal, said particles having a polyphase microstructure with the metals as one phase and compounds of the constituent metals with said B, N or P as at least one additional phase, said polyphase particles being coated with a thin oxide film.

This invention also comprises a method of making the above particles by heating particles consisting essentially of a single-phase alloy of a metal selected from at least one of iron, nickel, cobalt and from 0 to 20% chromium, super-saturated with at least one of B, N or P in an 3,567,525 Patented lVlar. 2, 1971 "ice amount less than the minimum amount required to form a compound with all of said metal, to a temperature below the sintering temperature, and for a time suflicient to increase the saturation magnetization to substantially a maximum, whereby compounds of said metal with said B, N or P are precipitated to transform said particles to a polyphase structure, said particles after transformation having substantially unchanged dimensions, said particles having a maximum dimension less than 4,u and having a coating of oxides.

DETAILED DESCRIPTION OF THE INVENTION The starting materials of the present invention containing boron are prepared by the borohydride reduction of the soluble metal salts of iron, nickel, or cobalt with alkali or alkaline earth borohydrides as taught by Miller and Oppegard.

The reduction is generally carried out in solution preferably approaching saturation, and at a temperature less than C. The borohydride solution preferably is added to the solution of metal salts rather than vice versa with agitation kept to the minimum required to ensure thorough mixing of the ingredients. To promote the formation of acicular particles, the reduction is accomplished in the presence of a magnetic field of at least 100 Oe. and preferably at least 1000 0e.

Iron, nickel or cobalt salts and mixtures thereof are essential ingredients of the reaction. Chromium salts can be added to the reaction mixture in which case metallic chromium is formed as a solid solution in the essential iron, nickel or cobalt. Chromium salts alone, however, are not reduced to the metal by wet reduction.

Where chromium is to be incorporated, the efiiciency of incorporation is greatest at 40 or greater. The presence of chromium increases the oxidation stability of the particles. In general, from 0.4 to 20% of chromium should be present, and preferably from 8 to 20%. Moreover, with such alloys as Fe/Cr/B the percentage of acicular particles increases with temperature of the reduction process.

Generally it is preferred to operate the process in a magnetic field of at least 100 0e. and preferably greater than 1000 oe. in order to promote the formation of acicular particles.

The heat treatment of the present invention modifies the metallurgical nature of the particles and greatly improves the saturation magnetization and certain other magnetic properties without substantially varying the particle dimensions.

When phosphorus is to be introduced, sodium hypophosphite, NaH PO is used as the reducing agent in basic ammoniacal solution (pH 9 or greater) and with a catalytic amount of palladium chloride PdCl in place of sodium borohydride system described above.

Likewise, nitrogen can be introduced by using hydrazine in ammonical aqueous solutions with catalytic amounts of palladous chloride.

Generally the solution medium is an aqueous system, but when some, or all, of the reactants have sparing solubility in water miscible organic solvent may replace at least part of the water.

The above systems are compatible with each other and mixtures of the above reducing systems can be used to introduce mixtures of the above elements in supersaturated solution in the metal components of the precipitated particles.

Palladous compounds also catalyse the reduction of the metal salts with alkali or alkaline earth metal borohydrides. When palladous salts are employed as a catalyst, small quantities of palladium metal are introduced into the resultant composition.

The temperature and time at which the single phase particles formed in the above precipitation process are heated to achieve polyphase structure varies with the nature and properties of the ingredients and cannot be generically defined in a manner common to all systems except that in all cases the temperature and time must be less than those conditions under which substantial sintering (i.e., substantial changes in particle dimension) occur. Conditions close to the sintering conditions are preferred.

The particular choice of conditions is illustrated by a detailed description in the case of a composition containing 59.6% Fe, 15.6% C and 4.1% B. The effects of heat treatment on the magnetic properties of this composition are shown in the appended drawings, FIGS. 3, 4 and 5.

Referring to these drawings, FIG. 3 is a plot of the saturation magnetization of the above composition after heat treatment plotted against time at the temperatures indicated.

FIG. 4 is a plot of o' /zr the remanence ratio, against time at the temperatures indicated. The remanence ratio gives some indication of the domain structures. For a random assembly of isotropic single domain particles, the remanence ratio is theoretically 0.5.

FIG. 5 shows a plot of the intrinsic coercivity, H as a function of time at the various temperatures indicated.

The intrinsic coercivity and saturation magnetization also indicate substantial single domain character in the optimally heat treated particles:

for single domain particles where p is the density of the particles (-8 for the compositions of this invention).

In FIGS. 3 to 5, at 300 C. the saturation magnetization increases slowly with time and evidently reaches a maximum after a time beyond the experiment. ,H and o' /o' follow a similar pattern over the 16 hour period of the data.

At 400 C., a reaches a maximum value at about 68 hours, and continues substantially constant. H reaches a maximum in about 1 /2 hours, and after 8 hours commences to degrade, indicating that sintering occurs. Observation of the particles using an electron microscope can likewise be employed to determine the amount of sintering by observing the change in particle dimensions. At 500 C. a reaches a maximum in under two hours; ,H however is degraded even at heating times of /2 hour, (T /0' is similarly degraded by sintering.

Similar curves will apply to other compositions except that the time and/or temperature scales may differ. In some instances ,H may increase little or even decrease slightly with time, but then will remain constant with time until, when sintering occurs, a significant decrease in ,H takes place.

When chromium is added to the systems in general, higher temperatures and/or longer times are needed to obtain optimum properties.

The heat treatment step can be performed in air but preferably an inert gas is employed, or hydrogen is used to provide a reducing atmosphere and prevent excessive oxidation of the particles.

After heat treatment when a reducing atmosphere is employed, it is desirable to passivate the particles by exchanging the hydrogen for an inert gas, preferably a noble gas such as argon containing a small amount of oxygen, suitably from 0.01 to 10% by volume. The passivation process is normally conducted at or close to ambient temperature and pressure, although this is not critical. Times for the process can range from 5 to about 4 hours, and depend on the oxygen content of the gas mixture.

Prior to the heat treatment process, both X-ray and electron diffraction show the diffraction pattern of the major metallic component, e.g., with iron alloys an X-ray diffraction pattern of u-iron is obtained. The compositions are evidently single phase with the minor metallic components and the metalloid or non-metals in solution.

Following the heat treatment process of the present invention, electron diffraction shows that the treated particles are polyphase and include metal compounds together with the metals.

Preferred compositions are those containing a substantial amount, preferably 50% or more of iron or cobalt or mixtures thereof, and optionally with minor amounts of nickel or chromium, which contain boron, i.e., the starting materials are prepared by borohydride reduction.

Compositions having improved magnetic properties can be obtained by the heat treatment process of this invention from the alloys described by Miller and Oppegard, however, chromium may also be incorporated in the alloys as indicated above.

When iron is the major component of the alloys, chromium may be present in any proportion up to 20% by Weight and boron preferably from 1 to 5.5% by weight. The chromium is generally at least 0.4% by weight, when present and most preferably from 5 to 20% by weight.

When cobalt is the major metallic component, the preferred range of chromium content is from 0 to 17% by Weight and boron from 1 to 5.6% by weight.

When nickel is the major metallic component, the preferred range of chromium content is 0 to 7% and the boron content is 1 to 5.6% by weight.

Compositions containing iron as a major component are preferred. Iron-cobalt-boron alloys in which the cobalt content is 30 to 35% are particularly useful for the manufacture of permanent magnets. Minor amounts of cobalt have been found beneficial in improving particle morphology, particularly when chromium is included to improve the stability of the magnetic properties under humid or moist conditions. Thus iron compositions containing 0.1 to 5% by weight of cobalt and from 8% to 20% by weight of chromium with 1 to 5.5% by weight of boron also form a preferred class of compositions.

Oxygen is always present in the as precipitated starting materials and is believed to occur in the form of oxides and/or hydroxides or hydrous oxides on the surfaces of the particles together with oxygen in the form of 'Water which is occluded or adsorbed in the particles. Substantially, all the water is eliminated, however, by baking at 200 C. and in thecompositions of this invention, the oxygen is principally present in the form of metal oxides, which are believed to be formed as a protective coating particularly during the passivation step.

The particles can be compacted by the techniques known in the field of powder metallurgy to form useful permanent magnets. Optionally small quantities of organic or inorganic binder can be present. Generally from about 2% to 30% by weight of binder based on the total composition is employed. Higher percentages of binder can be used, but are not generally desirable, since the binders are generally inert magnetically.

In the powder form the particles can be mixed with a film-forming binder and coated on a suitable substrate to form a magnetic recording member. A common form of a magnetic member, magnetic tape is shown in FIGS. 1 and 2 of the appended drawings.

FIG. 1 shows a plan view of a magnetic tape. FIG. 2 shows a cross section of the tape along the lines A-A. In the figure a substrate 1 is provided which is generally a flexible polymeric film having suitable mechanical properties, i.e., it should be flexible and dimensionally stable with time and under stress. Suitable polymeric film supports include film of polyethylene terephthalate which has been oriented by stretching biaxially, cellulose acetate and like materials. A coating of ferromagnetic particles in a binder 2 is coated onto the surface of the supporting film and calendered to a smooth, even layer.

This invention is further illustrated by the following examples, which should not, however, be construed as fully delineating the scope of this discovery. In these examplesparts and percentages are by weight unless otherwise specified. Magnetic properties were determined by packing the powder in tubes and placing them in an extraction magnetometer with an applied field of about 4400 cc. Saturation magnetization values, a are given in the examples as emu/ g. Saturation magnetization values for products with coercivities greater than 750/oe. were measured using a vibration magnetometer with a maximum field of 17,500 e.

EXAMPLE 1 A solution of 15.2 g. of NaBH dissolved in 250 ml. of distilled water was added dropwise to a solution containing 43.5 g. of FeSO -7H O and g. of Cr (SO -xH O dissolved in 500 ml. of distilled water in the absence of an external magnetic field. A vigorous exothermic reaction occurred forming 20 g. of a black magnetic powder. The powder was filtered, washed with 500 ml. of distilled water, washed with 500 ml. of acetone, and allowed to dry in air. The composition of the powder was 33.8% Fe, 14.1% Cr and 3.2% B, the balance consisting principally of oxygen present as metallic oxides and adsorbed moisture. The powder consisted essentially of equiaxed particles about 0.1 in diameter.

In the as-prepared condition, the powder had a saturation megnetization (a of 10.6 emu/g, a remanent megnetization (0-,) of 1.8 emu/ g. and an intrinsic coercivity H,) of 86 0e. This powder was heat treated in air at a temperature ranging from 275 to 300 C. for 1 hr. After heat treatment, the powder has a a of 71.1 emu/g, a a, of 13.5 emu/g., and an H of 333 oe.

EMMPLE 2 A solution of 7.6 g. of NaBH dissolved in 250 ml. of distilled water was added dropwise to a solution containing g. of and g. of CI2(SO4)3'XH2O dissolved in 500 ml. of distilled 'water in the absence of an external magnetic field. A black, magnetic powder was formed by an exothermic chemical reaction. The powder was filtered, washed, and dried in a manner similar to that described in Example 1. The chemical composition of the powder was 69.8% Fe, 12.7% Cr, and 2.2% B, the balance consisting principally of oxygen present as metallic oxides and adsorbed moisture, The powder consisted essentially of equiaxed particles about 0.05; in diameter.

6 EXAMPLES 34 Examples 3 through 7 illustrates the effect of heat treatment on increasing the a and a of iron-boron alloy powders containing 0 to 11.2 percent by weight chromium and also show the effect of chromium addition on preventing significant degradation of the a of the heat treated and passivated products when they are exposed to hot, humid atmospheres.

The iron-boron alloy powders containing 0 to 11.2% chromium were synthesized in the presence of a magnetic field of about 1500 cc. A two-liter beaker resting on the poles of a horseshoe magnet was charged with a solution containing salts of the metallic components of the desired alloy dissolved in 200 ml. of distilled water. A solution of 3.8 g. of NaBH in 100 ml. of distilled water was slowly added to the beaker in a period of time of about 10 min. During the addition of the NaBH solution, a vigorous exothermic reaction occurred forming a black, magnetic powder. The product was filtered, washed with water, and washed with acetone. After washing, the product was suspended in acetone for about 16 hrs. before final filtering and air drying. The compositions of the metallic salt solutions for synthesis of the products and the composition of products produced are summarized in Table I.

TABLE 1 Composition of metal salt solution Powder composition K C12(SO4)4. FGSO4.7H2O, 24H2O, g./200 Wt. per- Wt. per- Wt. per- Example g./200 ml. ml. cent Fe cent Cr cent B The powder products were composed principally of acicular particles having an average length ranging from about 1 to about 2 The air-dried, as-prepared products were heat-treated in hydrogen at temperatures ranging from 400 to 450 C. After heat treatment, they were cooled to ambient temperature and passivated by replacement of the hydrogen atmosphere with a gaseous mixture of argon containing about 1% by volume of oxygen. The powders were exposed to the argon-oxygen atmosphere for 20 to 72 hrs.

The product of Example 4 after heat treatment contained 79.4% Fe, 6.7% Cr and 3.4% B. The product of Example 5, after heat treatment contained 77.5% Fe, 8.1% Cr and 3.1% B.

The passivation treatment rendered the powders nonpyrophoric and also imparted resistance to degradation of a by hot, humid atmospheres. The effect of heat treatment and passivation on the magnetic properties of the powders is summarized in Table II.

Now: HT=heat treatment.

The as-prepared powder had a a of 77.9 emu/g, a

a, of 20.4 emu/ g. and an H,, of 271 oe. This powder was heat treated in purified H at 300 C. for 4 hrs. After heat treatment, the powder was pyrophoric. The magnetic properties measured in an argon atmosphere were a 99.0 emu/g; a 28.2 emu/g; and H 350 cc.

The stability of a of the heat treated and passivated powders was tested by exposing them to air at 65 C. and 50% relative humidity for 20 hrs. The results of the stability tests are reported in Table III, where the percent decrease in saturation magnetization is given under the 75 heading percent Aa TABLE III cobalt-boron powders and also illustrate the structural changes that occur during heat treatment. emu/g The powder products were prepared in an external mag- E 1 C -+9 ieg s a e P t A netic field by the dropwise addition of a solution contain- X m Y es 1 Y es 5 ing 3.8 g. of NaBH dissolved in 100 ml. of distilled wa- 4 5 g g ter into an aqueous solution of cobaltous and ferrous 116 78 salts. The synthesis conditions and composition of the 115 92 products obtained are summarized in Table V. 13.3 122 1 .5 4.9

liercent.

TABLE v Synthesis conditions/metal salt soln. comp, g./100 ml. Powder composition External FeSO C0012. C0804. magnetic Percent Percent Percent Example 7H2O 7H2O 7H2O field, 0e. Fe Co B 5 11 22. 3 4. 8 1, 300 51. 14.1 2. 1 12 22. 5. 5 2, 000 59. a 15.6 4. 16.7 11.2 1, 300 45.3 29.3 3.

EXAMPLES 8-10 After the powder products were filtered, Washed, and

These examples indicate the effect of heat treatment temperature on the magnetic properties of an iron-chromium-boron alloy powder and also illustrate the structural changes that occur during heat treatment.

An iron-chromium-boron powder was synthesized according te the procedure described for Example 7. The powder consisted essentially of acicular particles with an average length of about 2 and an average width of about 006 Its chemical composition was 66.7% Fe, 10.3% Cr, and 1. 5% B, the balance being principally composed of oxygen present as metallic oxides, hydroxides or absorbed moisture.

Samples of the as-prepared powder were heat treated in hydrogen for 4 hrs. at 300, 400, and 500 C. and then passivated in argon containing about 1% by volume oxygen. The effect of heat treatment on magnetic properties is summarized in Table IV.

Structural analysis by X-ray and electron diffraction techniques indicated that the principal phase present in the as-prepared product was a solid solution of chromium and boron dissolved in the body-centered-cubic structure of a-iron. No extra reflections that could be attributed to a metallic boride or a boron oxide were detected. Therefore the solid solution of iron and chromium is supersaturated with respect to boron because the alloy contained 1.5 percent by weight of B and the maximum solubility of boron in iron at room temperature under equilibrium conditions is much less than 0.01 percent by weight of boron (M. Hansen, Constitution of Binary Alloys, McGraw-Hill, p. 251, 1958). Analysis of electron diffraction patterns from the sample heat treated at 500 C. (Example 10) indicated that a metallic boride, M B, precipitated from the supersaturated solid solutions during heat treatment. The boride precipitate had the body-centered-tetragonal structure of Fe B (ASTM diffraction data card No. 3-1053), which according to Bertaut and Blum is isomorphous with a Cr B chromium boride 0F. Bertaut and P. Blum, C. R. Acad. Sci. Paris, 236,105 (1953)).

EXAMPLES 1 l-l 3 Examples 1'1 through 13 indicate the effect of heat treatments in hydrogen on increasing the (T5 of irondried by the general procedure described in Example 1, they were heat treated in hydrogen at 400 C. for 4 hrs. The products were then cooled to ambient temperature and passivated in argon containing about 1% by volume of oxygen. Data on the effect of heat treatment on the magnetic properties of the products appear in Table VI.

TABLE VI Magnetic properties Example Condition rs, emu/g. O /Ug 5H0, 0e.

11 As-prepared 44. 5 0. 53 1, 260 Heat treated 165 0. 51 1, 225

12 As-prepared 97 0. 42 790 Heat treated 168 0. 44 1, 000

13 b s-prepared 0.50 1, 210 neat treated 0. 51 1, 505

The products were composed of acicular particles with widths ranging from about 003 to about 0.06;.

Structural analysis by X-ray and electron difiraction techniques indicated that the principal phase present in the as-prepared iron-cobalt-boron products was a solid solution of cobalt and boron in body-centered-cubic oc-iI'OIl. Analyses of electron diifraction patterns from heat treated products indicated that a metallic M B boride had precipitated from the a-iron solid solution during heat treatment. The boride precipitate had the body-centeredtetragonal structures of Fe B (ASTM diifraction data card No. 3-1053) which is isomorphous with Co B (ASTM diifraction data card No. 3-0878). Both Fe B and Co B are ferromagnetic.

EXAMPLES 14-25 The tendency for a fine powder to sinter and agglomerate during heat treatment is a function of temperature, time at temperature, and powder composition. Examples 14 through 25 illustrate the effect of sintering and agglomeration on decreasing the coercivity and the remanence ratio of an iron-cobalt-boron alloy powder with a percent Fe to percent Co ratio of about 4 to 1 (59.6% Fe; 15.6% Co; 4.1% 3).

Samples of an iron-cobalt-boron powder prepared by the method described in Example 12 were subjected to heat treatments in hydrogen at temperatures ranging from 300 to 600 C. After heat treatment, the samples were cooled to ambient temperature and passivated in a gaseous mixture of argon plus about 1% oxygen. The coercivities, remanence ratio, and average particle dimensions of heat treated and passivated powders appear in Table VII. The

chemical analysis of some of the products is given in Table VIII.

TABLE VII Heat treatment Average Average Time, particle particle hr. iIL, oe. ri /a,- width, p length, p.

TABLE VIII.ANALYSIS OF HEAT TREATED PRODUCTS Before heat treatment, the powder had an H,, of 790 and a ar /0 ratio of 0.42. It was composed essentially of acicular particles with an average length of about 0.5 7 and an average width of about 0.05 14. There were no significant changes in the shape or size of the particles during four-hour heat treatments at temperatures up to 425 C. An increase in the temperature of a four-hour heat treatment from 425 C. to 500 C. increased the width of some particles by a factor of ten and decreased the coercivity of the product by a factor of four.

EXAMPLE 26 A metallic, magnetic powder was prepared by the addition of a solution of NaBH to a solution containing 33.4 g. of FeSO -7H O, 22.4 g. of CoSO -7H O and g. of K Cr (SO -24H O dissolved in 200 ml. of distilled water. The synthesis was performed in the presence of an external magnetic field of about 1500 oe. by the same general procedure described for Examples 3 through 7. The composition of the product was 37.6% Fe, 18.4% C0, 10.0% Cr. and 3.6% B, the balance being principally oxygen present as metallic oxides and adsorbed moisture. The powder consisted essentially of acicular particles with an average width of about 003 and an average length of about 0.3a.

1n the as-prepared condition, the powder had a a of 60 emu/g, a a /a ratio of 0.38, and an H of 440 oe. The powder was heat treated in hydrogen at 400 C. for 4 hrs., cooled to ambient temperature, and passivated in argon containing about 1% by volume of oxygen. After heat treatment and passivation, the powder had a a of 109.2 emu/g, a a /a ratio of 0.47, and an H of 949 oe. The composition was 41.4% Fe, 34.9% C0, 13.5% Cr and 4.2% B.

Although the structure of the as-prepared Powder appeared to be amorphous when examined with X ray radiation, a crystalline, body-centered-cubic phase with the structure of a-iron was detected by electron transmission diffraction. Analysis of electron diffraction patterns of the heat treated powder revealed the presence of the phase with the structure of Ot-II'OD. and a body-centered-tetragonal, M B, metallic boride.

EXAMPLE 27 A metallic, magnetic powder was prepared by the addition of a solution of 3.8 g. NaBH in 100 ml. of water to a solution containing 44.6 g. of FeSO '7H O and 10.5 g. of NiSO -6H O dissolved in 200 ml. of distilled water. The synthesis was performed in the presence of an external magnetic field of about 1500-oe. by the same general procedure described in Examples 3 through 7. The composition of the product was 56.4% Fe, 19.3% Ni, and 3.1% B, the balance being principally oxygen present as metallic oxides and adsorbed moisture. The powder consisted essentially of acicular particles with an average width of about 0.02 and an average length of about 0.4,u.

In the as-prepared condition, the powder had a a of 97.3 emu/g. a a' /J ratio of 0.44, and an H. of 1020 oe. The powder was heat treated in hydrogen at 400 C. for 4 hrs., cooled to ambient temperature and passivated in argon containing 1% by volume of oxygen. After heat treatment and passivation, the powder had a a of 139.5 emu/g, a a /a ratio of 0.39, and an H of 765 oe. The composition was 61.1% Fe, 21.6% Ni, 3.6% B.

EXAMPLE 28 A metallic, magnetic powder was prepared by the addition of a solution of 3.8 g. of NaBH, in ml. of water to a solution containing 44.6 g. of FeS0 -7H O, 10.5 g. of and 1 0f K2CI'2(SO4)424H2O dis solved in 200 ml. of water. The synthesis was performed in the presence of an external magnetic field of about 1500 oe. by the same general procedure described for Examples 3 through 7. The composition of the product was 48.6% Fe, 18.1% Ni, 1.75% Cr, and 3.5% B, the balance being principally oxygen present as metallic oxides and adsorbed moisture. The powder consisted essentially of equiaxed particles about 0.04 7 in diameter.

In the as-prepared condition, the powder has a a of 66 emu/g, a 0 /0 ratio of 0.43, and an H of 1040 oe. The powder was heat treated in hydrogen at 400 C. for 4 hrs., cooled to ambient temperature, and passivated in argon containing 1% by volume of oxygen. After heat treatment and passivation, the powder had a a of 109 emu/g, a a' /a ratio of 0.46, and an H of 1090 oe. The composition was 53.1% Fe; 22.3% Ni; 4.6% B.

EXAMPLE 29 A metallic, magnetic powder was prepared by the addition of a solution of 3.8 g. of NaBH in 100 ml. of water to a solution containing 44.6 g. of FeSO -7H O, 5.3 g. of NiSO -6H O, and 5.7 g. of CoSO -7H O dissolved in 200 ml. of distilled water. The synthesis was performed in the presence of an external magnetic field of about 1500 oe. by the same general procedure described for Examples 3 through 7. The composition of the product was 54.1% Fe, 7.7% Ni, 7.0% Co, and 3.3% B, the balance being principally oxygen present as metallic oxides and adsorbed moisture. The powder consisted essentially of acicular particles wth an average width of about 0.03 and an average length of about 0.2

In the as-prepared condition, the powder had a a of 32.5 emu/g, a a,/a ratio of 0.35, and an H,, of 500 oe. The powder was heat treated in hydrogen at 400 C. for 4 hrs., cooled to ambient temperature, and passivated in argon containing 1% by volume of oxygen. After heat treatment and passivation, the powder had a a of 86 emu/g, a er /0' ratio of 0.35, and an H of 564 oe. The composition was 56.4% Fe, 8.9% Ni, 12.1% Co, 5.2% B.

- EXAMPLE 30 A metallic, magnetic powder was prepared by the addition of a solution of 3.8 g. of NaBH in 100 ml. of water to a solution containing 44.6 g. of FeSO -7H O, 5.3 g. of NiSO -6H O, 5 .7 g. of CoSO -7H O and 1 g. of K2CI2(SO4)4'24H2O dissolved in ml. of water. The synthesis was performed in the presence of an external magnetic field of about 1500 oe. by the same general procedure described for Examples 3 through 7. The composition of the product was 50.1% Fe, 6.8% Ni, 6.5% Co, 1.9% Cr, and 3.1% B, the balance being principally oxygen present as metallic oxides and adsorbed moisture. The powder consisted essentially of equiaxed particles about 0.02/1. in diameter.

In the as-prepared condition, the powder had a a of 68.3 emu/g, a 03/ a ratio of 0.40, and an ,H of 825 oe. The powder was heat treated in hydrogen at 400 C. for 4 hrs., cooled to ambient temperature, and passivated in argon containing 1% by volume of oxygen. After heat treatment and passivation, the powder had a a of 119.6 emu/g., a a /a of 0.41, and an H of 1020 oe. The composition was 52.8% Fe, 9.3% Ni, 8.8% Co, 3.7% B.

EXAMPLE 31 A metallic powder was prepared by the addition of a solution of NaBH 1 g. in 100 ml. H O) to a solution containing 56.2 g. of CoSO -7H O dissolved in 200 ml. of distilled water. The synthesis was performed in the presence of an external magnetic field of about 1500 oe. by the same general procedure described for Examples 3 through 7. The composition of the product was 79.71% Co and 5.6% B, the balance being principally oxygen present as metallic oxides and adsorbed moisture.

In the as-prepared condition, the powder had a a of 34 emu/g, a a /o' ratio of 0.235 and an H of 35 oe. The powder was heat treated in hydrogen at 300 C. for 4 hrs., cooled to ambient temperature and passivated in argon containing 1% by volume of oxygen. After heat treatment and passivation, the powder had a a of 65, a a /a ratio of 0.42, and an H,, of 275 oe.

EXAMPLE 32 A metallic powder was prepared by the addition of a solution of NaBH, (3.8 g. in 100 ml. H O) to a solution containing 28.1 g. of Co.SO -7H O and 26.3 g. of NiSO -6H O dissolved in 200 ml. of distilled water. The synthesis was performed in the presence of an external magnetic field of about 1500 oe. by the same general procedure described for Example 3 through 7. The composition of the product was 48.6% C0, 30.3% Ni and 4.1% B, the balance being principally oxygen present as metallic oxides and adsorbed moisture.

In the as-prepared condition, the powder had a a of 8 emu/g, a a /o' ratio of 0, and an H of 0. The powder was heat treated in hydrogen at 400 C. for 4 hrs., cooled to ambient temperature, and passivated in argon containing 1% by volume oxygen. After heat treatment and passivation, the powder had a a of 52 emu/g, a a /o' ratio of 0.423, and an H,, of 580 oe.

EXAMPLE 3 3 A metallic, magnetic powder was prepared by the addition of a solution of 3.8 g. of NaBH in 100 ml. of water to a solution containing 45 g. of CoSO '7H O, 0f NISO46HZO, and 1 of K Cr (SO -24H O dissolved in 200 ml. of distilled water. The synthesis was performed in the presence of an external magnetic field of about 1500 oe. by the same general procedure described for Examples 3 through 7. The composition of the product was 61.2% Co, 7.5% Ni, 0.4% Cr, and 7.4% B, the balance being principally oxygen present as metallic oxides and adsorbed moisture. The powder consisted essentially of equiaxed particles about 0.05 1 in diameter.

In the as-prepared condition, the powder had a a of 19 emu/g, a a /o' ratio of 0.16, and an H of 30 oe. The powder was heat treated in hydrogen at 400 C. for 4 hrs., cooled to ambient temperature, and passivated in argon containing 1% by volume of oxygen. After heat treatment and passivation, the powder had a a of 77 emu/g, a a' /a ratio of 0.40, and an ,H,, of 630 oe.

EXAMPLE 34 A metallic powder was prepared by the addition of a solution of 3.8 g. NaBH in 100 ml. of water to a solution containing 52.4 g. of NiSO -6H O dissolved in 200 ml. of distilled water. The synthesis was performed in the presence of an external magnetic field of about 1500 oe. by the same general procedure described for Examples 3 through 7. The composition of the product was 12 68.7% Ni, and 5.3% B, the balance being principally oxygen present as metallic oxides and adsorbed moisture. The powder consisted essentially of equiaxed particles about 0.02 in diameter.

In the as-prepared condition, the powder had a a of 2.1 emu/ g. and an H,, 20 oe. The powder was heat treated in hydrogen at 400 C. for 4 hrs., cooled to ambient temperature, and passivated in argon containing 1% by volume of oxygen. After heat treatment and passivation, the powder had a a of 30 emu/g. a a /a ratio of 0.27, and an H,, of 142 oe.

EXAMPLE 3 5 A metallic powder was prepared by the addition of a solution of 3.8 g. NaBH, in 100 ml. of water to a solution containing 57.4 g. of NiCl -6H O and 1 g. of CrCl -6H O dissolved in 200 m1. of distilled water. The synthesis was performed in the presence of an external magnetic field of about 1500 oe. by the same general procedure described for Examples 3 through 7. The composition of the product was 74.5% Ni, 3.5% Cr, and 5.4% B, the balance being principally oxygen present as metallic oxides and adsorbed moisture. The powder consisted of equiaxed particles about 0.02 1. in diameter.

In the as-prepared condition, the powder had a a of 1.5 emu/g, a a /o' ratio of 0.07, and an H 20 oe. The powder was heat treated in hydrogen at 400 C. for 4 hrs., cooled to ambient temperature, and passivated in argon containing 1% by volume of oxygen. After heat treatment and passivation, the powder had a a of 29.8 emu/g, a o' /o' ratio of 0.26, and an H of 112 oe.

Only one broad, intense diifraction line with a d spacing of about 2 A. was detected in X-ray and electron diffraction of the as-prepared nickel-chromium-boron powder. However, analysis of X-ray diffraction patterns of the heat treated product indicated the presence of a phase with the structure of face-centered-cubic nickel and an orthorhombic, M B, boride phase. The X-ray pattern for the M B phase fit the structure for Ni B found by S. Rundqvist (Acta. Chem. Scand., 13, p. 1193, 1959).

EXAMPLE 36 This example illustrates the fabrication of heat treated, iron-chromium-boron alloy powder into a magnetic recording tape.

Several duplicate batches of an iron-chromium-boron alloy powder were prepared by the technique described in Example 7 and blended in a rotating plastic canister containing poly(tetrafluoroethylene) balls. The powder blend 'Was heat treated in hydrogen at 450 C. for 4 hrs. and then passivated in argon containing about 1% by volume oxygen. In the heat treated and passivated condition, the powder had a a of 128 emu/g, a a a ratio of 0.38, and an H,, of 560 oe.

The heat treated and passivated powder was ground with 20- to 30-mesh sand in a slurry of tetrahydrofuran plus soya lecithin for 2 hrs. and then mixed in the sand grinder with a binder consisting of 50%, by weight, of a soluble polyester-urethane resin made from diphenylmethane diisocyanate, adipic acid and 'butanediol, and 50% of a vinylidene chloride/acrylonitrile /20 copolymer. The binder-powder system contained about 30 volume percent of powder. After mixing, the binderpowder slurry was filtered through a 2-;/. screen to remove the sand. Coatings of the filtered slurry were then spread on a 1.5-mil thick film of poly(ethylene terephthalate). The coated films, which were about 3 inches wide and 30 inches long, were passed between the poles of two plate magnets that created a field of about 800 oe. parallel to the long direction of the tape before the coating dried. The tape was then dried in air for about 24 hrs. and dried in a vacuum desiccator for about 16 hrs.

The magnetic tape fabricated from the iron-chromiumboron powder had a 5,. /2" of 1.49 maxwells, a B /B of 0.70, and an H,, of 465 oe.

13 EXAMPLE 37 This example illustrates the fabrication of a heattreated, iron-cobalt-boron alloy powder into a magnetic recording tape.

Several duplicate batches of an iron-cobalt-boron powder were prepared by the technique described in Example 12 and blended and compacted in a rotating plastic canister containing poly(tetrafluoroethylene) balls. The powder blend was heat treated in hydrogen at 400 C. for 4 hrs. and then passivated in argon containing about 1% by volume of oxygen. In the heat treated and passivated condition the powder had a a of 168, a a /o' ratio of 0.46, and an H of 840 oe.

The heat treated and passivated powder was ground in a sand shaker with 20- to 30-mesh sand in a slurry of tetrahydrofuran plus soya lecithin for 1 hr. and then mixed in the sand shaker with a binder consisting of 50%, by weight, of a soluble polyester-urethane resin made from diphenylmethane diisocyanate, adipic acid and butanediol, and 50% of a vinylidene chloride/acrylonitrile 80/20 copolymer. The binder-powder system contained about 40 volume percent of powder. After mixing, the binder-powder slurry was filtered through a 10-,u screen to remove the sand. Coatings of the filtered slurry were then spread on a 1.5 mil thick film of poly(ethylene terephthalate). The coated films, which were about 3 inches wide and 30 inches long, were passed between the poles of two plate magnets that created a field of about 800 Oe. parallel to the long direction of the tape. The tape was then dried in air for about 24 hrs. and dried in a vacuum desiccator for about 16 hrs. The magnetic tape fabricated from the Fe-Co-B powder had a 4),- /2" of 2.40 maxwells, a B of 2480 gauss, a B /B of 0.69 and an H of 720 oe.

EXAMPLE 38 An iron-cobalt-boron powder was prepared by the addition of a solution of NaBH to a solution containing 33.4 g. of FeSO -7H O and 22.4 g. of CoSO -7H O dissolved in 200 ml. of distilled water. The synthesis was performed in the presence of an external magnetic field of about 1500 oe. by the same general procedure described for Examples 3 through 7. The composition of the product was 50.6% Fe, 28.5% C0, and 3.5% B, the balance being principally oxygen present as metallic oxides and adsorbed moisture. The powder consisted essentially of acicular particles with an average width of about 0.04;; and an average length of about 0.7

In the as-prepared condition, the powder had a a of 119 emu/g, a ar /0' ratio of 0.47 and an H of 1260 oe. The powder was heat treated in hydrogen at 400 C. for 4 hrs., cooled to ambient temperature, and passivated in argon containing 1% by volume of oxygen. After heat treatment of passivation, the powder has a a of 186 emu/g., a a /a ratio of 0.49, and an H,, of 1150 oe.

EXAMPLE 39 Several synthesis runs of an iron-chromium-boron alloy powder were prepared by the dropwise addition of a 1 molar NaBH solution into a solution containing 1 I mol/l. of FeSO -7H O and 0.125 mol/l. of

K2CI'2(SO4)424H20 The solution containing FeSO -7H O and K2Cr2(SO4)4 was maintained at a temperature of 50 C. and was situated above the poles of a magnet having a field strength of about 1700 oe. during the addition of the NaBH solution, a vigorous exothermic reaction occurred forming a black, magnetic powder. The powder product was filtered, washed with water and washed with acetone. After washing the product was suspended in acetone for 16 hrs. before final filtration and air drying.

The synthesis runs were blended in a rotating plastic TABLE 1X Heat treatment Magnetic properties Temp., C. Time, hr. r11. 0e. a emu/g. ar /a,

Before heat treatment, the powder had an H of 385 oe., a a of 84 and a a /o' ratio of 0.35. It was composed essentially of acicular particles with an average width of about 0.07 and an average length of about 0.5 Examination of the heat treated products in an electron microscope failed to reveal any changes in particle shape or size which would be indicative of sintering. The high H and a /a ratios of the heat treated products are also indicative of the fact that sintering has not occurred.

EXAMPLE 40 A 2-liter beaker resting on the poles of a permanent magnet (1500 oe.) was charged with a solution containing 56.2 g. of CoSO -7H O dissolved in 200 ml. of distilled water and 200 ml. of concentrated NH OH. A solution of 3.8 g. NaBH 21.2 g. NaH PO and 10 ml. NH NH -H O in 200 ml. of distilled water was added. The accelerator (10 ml. Pd'Cl 1%) was added and the reaction mixture was allowed to stand for 30 minutes. It was then filtered and the product Was washed with 500 ml. of distilled water and 500 ml. of acetone. After washing, the product was suspended in acetone for about 16 hrs. before final filtering and air-drying. The composition of the product (6.2 g.) was 84.76% Co, 2.55% B, 5.12% P, and 0.66% N, the balance being principally oxygen present as metallic oxides and adsorbed moisture.

In the as-prepared condition, the powder had a a of 50 emu/g, a a /a ratio of 0.129 and an H of 130. The powder was heat treated in hydrogen at 400 C. for 4 hrs., cooled to ambient temperature and passivated in argon containing 1% by volume of oxygen. After heat treatment and passivation, the powder has a a of 86 emu/g, a a /o' ratio of 0.211 and an H of 145.

EXAMPLE 41 A two-liter beaker was charged with a solution containing 56.2 g. of CoSo -7H O, 1 g. K Cr (SO -24H O and 5 g. of the disodium salt of ethylenediamine tetracetic acid dissolved in 200 ml. of distilled water and 200 ml. of concentrated NH OH. A solution of 3.8 g. of NaBH in 100 ml. of distilled water was added slowly to the beaker in a period of time of about 10 minutes. The accelerator, 10 ml. PdCl (1% solution) was added and the reaction mixture was allowed to stand for two hours. The reaction mixture was filtered and the product was washed with ml. dilute NH OH and ml. of acetone. After washing, the product was suspended in acetone for about 16 hrs. before final filtering and airdrying. The composition of the product (4.0 g.) was 79.1% Co, 2.4% Cr, 1.8% Pd and 4.6% B, the balance being principally oxygen present as metallic oxides and adsorbed moisture.

In the as-prepared condition, the powder had a a of 67 emu/g., a ar /0' ratio of 0.14 and an H of 65. The powder was heat treated in hydrogen at 400 C. for 4 hrs., cooled to ambient temperature and passivated in argon containing 1% by 'volume of oxygen. After heat treatment and passivation, the powder has a a of 106 emu/g, a a /a ratio of 0.26 and an H,. of 260.

Before heat treatment, the structure of the product as determined by X-ray powder patterns taken with C Kat-radiation was that of hexagonal-close-packed cobalt. No extra diffraction lines which could be attributed to a boron containing phase or a body centered-cubicchromi ium 'phase were detected in the pattern from the aschemically prepared powder. After heat treatment the product consisted of a mixture of a hexagonal-closepacked cobalt phase, a face-centered cubic cobalt phase and a boride phase with the structure of Co B (ASTM X-ray data card No. 13-133 EXAMPLE 42 The procedure described below was used in the following two examples.

A two-liter beaker resting on the poles of a permanent magnet 1500 oe.) was charged with a solution containing 55.6 g. of FeSO -7H O dissolved 200 ml. of distilled water. A solution of NaBH and NaH PO in 150 ml. of distilled water was added slowly to the beaker in a period of time of about 10: minutes. The reaction mixture was filtered and the product was washed with 500 ml. of distilled water and 500 ml. of acetonefAfter washing, the product was suspended in acetone for about 16 hrs. before 'final filtering and air-drying.

The amounts of reducing agent employed for preparations -A and B are shown in Table X. The composition of the products is shown in Table XI. Magnetic data for the materials. before and after heat treatment are given in Table XIIJI V The powders were heat treated in diydrogen at 400 C. for 4 hrs., cooled to ambient temperatures and passivated in argon containing 1% by volume oxygen.

TABLE X Niimber NaBHi, g. N aHzPQg, g. ReslLt A 3.8; 2.1 3.0 g. black magnetic powder. B 3.8 4. 2 2.8 g. black magnetic powder.

TABLE XI.- Preparation of Fe-B-P ANA- LYTICAL QATA EXAMPLE 43 A two-liter beaker resting on the poles of a horseshoe magnet (1500 oe.) was charged with a solution containing 56.2 g. of CoSO '7H O dissolved in 200 ml. of distilled water and 200 ml. of concentrated ammonium hydroxide. A solution of 3.8 g. of N aBH in 100 ml of distilled water was slowly added to the beaker in a period of time of about: 10 min. In contrast to reactions carried out under acidic conditions, there was no violent exothermic reaction. On standing gas was slowly evolved and a black, magnetic powder precipitated. After standing for .16 hours the reaction mixture was filtered and the product was washed with 500 ml. of distilled water and 500 ml. of acetone. After washing, the product was suspended in acetone for about 16 hrs. before final filtering and air drying. 'The composition of the product (3.4 g.) was 77.78% Co and 4.43% B, the balance being principally oxygen present as metallic oxides and adsorbed moisture.

In the as-prepared condition, the powder had a a of 63 emu/g, a o' /o' ratio of 0.127 and an H of 38.5. The powder was heat treated inhydrogerr at 400 C. for 4 hrs., cooled'to ambient temperature, and passivated in argon containing 1% by volume of oxygen. After heat treatment and passivation, the powder has a a of 112 emu/g, a a ia ratio of 0.250, and an H of 240 oe.

EXAMPLE 44 I 20 with 506 ml. of distilled water and 500 ml. of acetone,

and allowed to air dry. The composition of the product (2.7 g.) was 78.6% C0, 11.2% Ni, 2.0% P, 4.25% Pd and 0.84% N, the balance being principally oxygen present as metallic oxides and adsorbed moisture.

In the as-prepared condition, the powder had a a of 97 emu/g, a a /a ratio of 0.35 and an H of 590. The powder was heat treated in hydrogen at 400 C. for 4hrs., cooled to ambient temperature and passivated in argon containing 1% by volume of oxygen. After heat treatment and passivation, the powder had a a of 106, a (T /0' ratio of 0.38 and an H of 499 oe.

EXAMPLE 45 A two-liter beaker resting on the poles of a horseshoe magnet (1500 oe.) was charged with a solution containing 28.1 g. of CoSO -7H O and 28.1 g. NiSO -6H O dissolved in 200 m1; of distilled water. A solution of 5.8 g; of NaBH and 10 ml. NH NH z-H o in 100 ml. of distilled water was slowly added 'to the beaker in a period of time of about 10 minutes. The reaction mixture was filtered and the product was washed with 500 mi; of distilled water and 500 ml. of acetone. After washing, the product was suspended in acetone for about 16 hrs. before final filtering and air drying. The composition of the product (13.1 g.) was 35 .10% C9, 21.27% Ni, 5.41% B and 1.05% N, the balance being principally oxygen present as metallic oxides and adsorbed moisture.

In the as-prepared condition, the powder had a a of 2.2 emu/g, a a /a' ratio of 0 and an H of 0. The powder was heat treated in hydrogen at 400 C. for 4 hrs., cooled to ambient temperature and passivated in argon containing 1% by volume of oxygen. After heat treatment and passivation, the powder had a a of 75 emu/g, a a a ratio of 0.32'0'and an H of 390 oe.

EXAMPLE 46 A two-liter beaker was charged with a solution containing 56.2 g. CoSO -7H O dissolved in 100 ml. of distilled water and 100 ml. of concentrated NH Q H. A solution of 21.2 g. of NaH PO in 50 ml. of distilled water was added to the Co++ solution. The accelerator 10 ml. E'dClz, 1%) was added and the reaction mixture was heated to 100 C. for liminutesi It was then allowed .to stand ,at room temperature for 16 hoursJIhe reaction mixture was filtered and the product was washed with 500 ml. of distilled water and 500 ml. of acetone. After washing, the product was suspendedin acetone for about 16 hrs. before final filtering and air-drying. The composition of .the product (19.1 g.) was 46.04% Co, 7.78%? and 40.2% 0. I if In the as-prepared condition, the powder had a a of 22.6 emu/g, a a Za ratio of 0.155, and an H of 375. The powder was heat treated in hydrogen at 400 C. for 4 hours, cooled to ambient temperature and passivated in argon containing 1% by volume of oxygen.

After heat treatment and passivation, the powder has a a of 53, a (r /a ratio of 0.208 and an I-I of 394.

EXAMPLE 47 A two-liter beaker resting on the poles of a horseshoe magnet (1500 e.) was charged with a solution containing 33.4 g. FeSO '7H O, 22.4 g. CoSO -7H O and 2 g. (NH HPO dissolved in 200 ml. of distilled water. A solution of 3.8 g. of NaBH in 100 ml. of distilled water was slowly added to the beaker in a period of about 10 minutes. The reaction mixture was filtered and the product Was washed with 500 ml. of distilled water and 500 ml. of acetone. After washing, the product was suspended in acetone for about 16 hrs. before filtering and air-drying. The composition of the product (5.9 g.) was 42.82% Fe, 28.31% Co, 2.77% P and 4.52% B, the balance being principally oxygen present as metallic oxides and adsorbed moisture.

In .the' as-prepared condition, the powder had a 0' of 95 emu/g, a o' /a' ratio of 0.378, and an H of 630 oe. The powder was heat treated in hydrogen at 400 C. for 4 hours, cooled to ambient temperature and passivated in argon containing 1% by volume of oxygen. After heat treatment and passivation, the powder has a a of 123 emu/g, a (T /0' ratio of 0.495 and an H of 1330.

EXAMPLE 48 A two-liter beaker was charged with a solution containing 11.2 g. CoSO -7H O and 47 g. NiSO -6H O dissolved in 200 ml. of distilled water and 200 ml. of concentrated NH OH. Hydrazine hydrate (10 ml.) and the accelerator (10 ml. PdCl 1%) were added and the reaction mixture allowed to stand for 2 hours. It was then filtered and the product was washed with 125 ml. dilute NH OH and 125 ml. of acetone. After washing, the product was suspended in acetone for about 16 hrs. before final filtering and air drying. The composition of the product (1.1 g.) was 73.75% Co, 12.88% Ni, 6.32% Pd and 1.44% N, the balance being principally oxygen present as metallic oxides and adsorbed moisture.

In the as-prepared condition, the powder had a 0' of 98 emu/g, a o' /a ratio of 0.224, and an ,H of 280 oe. The powder was heat treated in hydrogen at 300 C. for 4 hours, cooled to ambient temperature and passivated in argon containing 1% by volume of oxygen. After heat treatment and passivation, the powder has a a of 115 emu/g, a o' /o' ratio of 0.243 and an H of 290.

EXAMPLE 49 A two-liter beaker was charged with a solution containing 47.6 g. of CoCl -6H O dissolved in 200 ml. of distilled water and 200 ml. of concentrated NH OH. A solution of 3.8 g. of NaBH in "100 ml. of distilled water and ml. of NH NH -H O was added to the beaker and the reaction mixture was allowed to stand for two hours. It was then filtered and the product was washed with 125 ml. of dilute NH OH and in acetone for about 16 hours before final filtering and air drying. The composition of the product (2.5 g.) was 85.02% Co, 1.80% B and 0.27% N, the balance being principally oxygen present as metallic oxides and adsorbed moisture.

In the as-prepared condition, the powder had a a of 109 emu/g, a o' /tr ratio of 0.23 and an H of 170 cc. The powder was heat treated in hydrogen at 400 C. for 4 hrs. cooled to ambient temperature and passivated in argon containing 3% by volume of oxygen. After heat treatment and passivation, the powder has a as of 128 emu/g, a (T /0' ratio of 0.22 and an H of 190 oe.

Since obvious modifications and equivalents of the invention will be evident to those skilled in the art, we propose to be bound solely by the appended claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

-1. A ferromagnetic composition comprising polyphase particles having a maximum dimensions of about 4 microns, said particles consisting essentially of at least one metal consisting of iron, cobalt and nickel and up to 20% of chromium and at least one element selected from B, N or P in an amount less than the minimum amount required to form a compound with all of said metal, said particles having a polyphase microstrncture with the metals as one phase and compounds of the constituent metals with said B, N or P as at least one additional phase, said polyphase particles being coated with a thin oxide film.

2. Composition of claim 1 in which said element is boron.

3. Composition of claim 1 in which said particles are acicular, having a cross-sectional dimension of 0.01 to 1 micron, a length of 0.05 to 4 microns, the ratio of length to cross-sectional dimension being at least 3:1.

4. Composition of claim 2 wherein said particles are iron with from 0.4 to 20% chromium and 1 to 8% of boron.

5. Composition of claim 2 wherein said particles are iron with from 0.1 to 5% by weight of cobalt, 8 to 20% of chromium and 1 to 5.5% of boron.

6. Composition of claim 1 in which the panticles are iron with 30 to 35% by weight of cobalt and 1 to 5.5% of boron.

7. A magnetic recording member having as its active magnetic element the composition of claim 1.

8. A magnetic recording member having as its active magnetic element the composition of claim 2.

9. A permanent magnet composed of the particles of claim 1.

10. A permanent magnet composed of the particles of claim 2.

References Cited UNITED STATES PATENTS 3,026,215 3/1962 Fukuda et al 148!105X 3,188,247 6/1965 De Vos et a1 148105X 3,206,338 9/1965 Miller et al 148-105 3,348,982 10/1967 Dunton 1'48105 L. DEWAYNE RUTLEDGE, Primary Examiner G. K. WHITE, Assistant Examiner US Cl. X.R. 

